NR-U Initial Access via Cyclic-Wrapped SS/PBCH Indices

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Solution Overview

Problem

The challenge in New Radio (NR) unlicensed spectrum access is to reduce initial access latency and support random access, particularly contention-based random access channel (RACH), while efficiently multiplexing physical random access channel (PRACH) with physical uplink control channel (PUCCH) and physical uplink shared channel (PUSCH), especially in standalone NR-U operation, where uplink control information (UCI) needs to be transmitted on unlicensed bands.

Innovation Solution

A method involving a processor receiving synchronization signal and PBCH blocks with cyclic-wrapped indices based on listen-before-talk (LBT) results, allowing opportunistic initial access opportunities and allocating RACH resources strategically to reduce LBT time, enabling multiple PRACH transmissions and autonomous PUCCH transmissions on pre-configured or shared resources, and prioritizing channels through different preambles and access durations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If listen-before-talk (LBT) is implemented for fair coexistence in unlicensed spectrum, then channel access fairness is improved, but initial access latency increases and becomes unpredictable

Engineering Contradiction:

Improvechannel access fairnessVSAvoidinitial access latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The base station performs LBT and determines channel availability in advance before transmitting synchronization signals and allocating RACH resources. This preliminary channel assessment allows the system to prepare access opportunities proactively, reducing the unpredictable latency that would otherwise occur during the random access process when devices perform LBT independently.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The random access procedure is segmented into multiple opportunities with different LBT requirements. Some RACH opportunities are configured with relaxed LBT conditions (e.g., shorter contention window sizes or different priority levels) to enable faster access, while others maintain stricter LBT for fairness. This segmentation allows devices to attempt access through multiple pathways with different latency characteristics.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If RACH resources are allocated to support random access in NR-U, then random access capability is improved, but channel access efficiency deteriorates due to LBT constraints

Engineering Contradiction:

Improverandom access capabilityVSAvoidchannel access efficiency

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The system dynamically adjusts RACH resource allocation and LBT parameters based on channel conditions and traffic requirements. The base station can configure different RACH occasions with varying LBT requirements, allowing the random access mechanism to adapt to changing unlicensed spectrum conditions while maintaining both capability and efficiency.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

LBT parameters such as contention window size, priority level, and deferment duration are changed based on the specific RACH opportunity and channel conditions. By varying these parameters across different RACH occasions, the system optimizes the balance between supporting diverse random access needs and maintaining efficient channel utilization.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If multiple channels (PRACH, PUCCH, PUSCH) are multiplexed on unlicensed bands, then uplink control information transmission is improved, but channel access complexity increases

Engineering Contradiction:

Improveuplink control information transmissionVSAvoidchannel access complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Multiple uplink channels (PRACH, PUCCH, PUSCH) are merged into shared resource pools with unified LBT procedures. Instead of implementing separate LBT mechanisms for each channel type, the system combines them into a single channel access framework where devices contend for shared resources, reducing the complexity of managing multiple independent access procedures.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The LBT mechanism is designed as a universal procedure that handles multiple channel types (random access, control information, data) through a single unified framework. This multi-functional approach allows the same LBT logic to govern access to different uplink channels, simplifying the overall channel access complexity while maintaining the ability to transmit various types of uplink information.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11490428B2Initial access in new radio unlicensed spectrum

Publication Date: 2022.11.01 MEDIATEK INC

AI summary

Techniques and examples of design for initial access in New Radio (NR) unlicensed spectrum (NR-U) are described. An apparatus receives from a base station of a wireless network which transmits one or multiple synchronization signal and PBCH blocks (SS/PBCH blocks) whose indices are indicated in a cyclic-wrapped order subject to a result of listen-before-talk (LBT) in NR-U. The apparatus also transmits a random access request on random access channel (RACH) resources allocated by the base station.